It is another technical object of the invention to provide a Gate Valves in which a mounting structure of a gate and a shaft to each other is improved and second moment of area of the gate is increased to thereby reduce flection at opposite ends of the gate.

It is another technical object of the invention to provide a GATE VALVES in which weight of the gate is reduced by enhancement of mechanical strength of the gate and an amount of deformation of the gate when a seal is provided is reduced to evenly apply a sealing force with a small valve closing force to thereby carry out sealing with a small amount of leakage.

It is yet another technical object of the invention to provide a gate valve in which, because it is unnecessary to strongly press the gate against the valve seat, it is possible to use a small-sized cylinder device for pressing the gate against the valve seat with a small force and therefore it is unnecessary to increase overall member strength.

To achieve the above objects, in a gate valve of the invention, a central portion of a longer side of a rectangular gate being mounted to a tip end of a shaft operated by driving of a cylinder device and the gate being pressed against a valve seat provided around a rectangular valve opening by tilting the shaft with tilting means after the gate is moved to a position facing the valve opening by driving the shaft with the cylinder device, the gate is formed to have an uneven wall thickness including a large thickness in a vicinity of a fulcrum portion connected to the shaft and a small thickness on each of opposite end portion sides.Cast Gate, Globe, Check Valves

In the above gate valve, it is effective that a connecting hole for connecting the shaft for driving the gate is formed in a fulcrum portion of the gate, the connecting hole is formed such that a thickness of the gate on a side of a contact face with the valve seat is large and that a thickness of the gate on a side of an opposite face is small, and the tip end of the shaft is inserted into the connecting hole to connect the gate to the shaft.

In the gate valve having the above structure, because the thickness of the fulcrum portion at the center of the gate which receives the maximum bending stress due to the force from the shaft is increased to give the gate an uneven wall thickness for suppressing flection at the opposite end portions due to the bending moment, the mechanical strength of the gate itself is effectively enhanced and the gate in which flection of the opposite end portions is small can be formed as a lightweight gate. Because the connecting hole is formed in the gate in connecting of the gate and the shaft and because the thickness receiving tensile stress on the side of the contact face with the valve seat is increased and the thickness on the opposite side receiving compression is reduced to increase the second moment of area, it is possible to further reduce flection of the opposite end portions of the gate.

Moreover, because an amount of deformation of the gate when a seal is provided is reduced by enhancement of the mechanical strength of the gate, it is possible to evenly apply a sealing force with a small valve closing force to carry out sealing with a small amount of leakage. Furthermore, because it is unnecessary to strongly press the gate against the valve seat, it is possible to use the small-sized cylinder device and it is unnecessary to increase overall member strength.

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